USGS Mineral Resources Program The Rare-Earth Elements— Vital to Modern Technologies and Lifestyles Until recently, the rare-earth elements (REEs) were familiar to a relatively As part of a broad mission to conduct research small number of people, such as chemists, geologists, specialized materials and provide information on nonfuel mineral scientists, and engineers. In the 21st century, the REEs have gained visibility resources, the U.S. Geological Survey (USGS) through many media outlets because (1) the public has recognized the critical, supports science to understand the following: specialized properties that REEs contribute to modern technology, as well as (2) China’s dominance in production and supply of the REEs and (3) inter- • Where and how concentrations of rare- national dependence on China for the majority of the world’s REE supply. earth elements form in the Earth’s crust; Since the late 1990s, China has provided 85 – 95 percent of the world’s • Where undiscovered/undeveloped resources REEs. In 2010, China announced their intention to reduce REE exports. During of rare-earth elements may occur; this timeframe, REE use increased substantially. REEs are used as components in high technology devices, including smart phones, digital cameras, computer • Trends in the supply and demand of hard disks, fluorescent and light-emitting-diode (LED) lights, flat screen rare-earth elements domestically and televisions, computer monitors, and electronic displays. Large quantities of internationally; some REEs are used in clean energy and defense technologies. Because of the many important uses of REEs, nations dependent on new technologies, • How undisturbed and mined rare-earth such as Japan, the United States, and members of the European Union, reacted deposits interact with the environment. with great concern to China’s intent to reduce its REE exports. Consequently, exploration activities intent on discovering economic deposits of REEs and bringing them into production have increased. List of the rare-earth elements found in natural deposits—the “lanthanides” plus yttrium. [Average abundance (concentration) in the earth’s crust What are the Rare-Earth Elements? (in parts per million) from Lide (2004, CRC handbook The REE group is composed of 15 elements that range in atomic number of physics and chemistry, 85th edition). For comparison, from 57 (lanthanum) to 71 (lutetium) on the periodic table of elements, and are average crustal abundances for gold, silver, lead, and copper are 0.004, 0.075, 14, and 60 parts per million, officially referred to as the “lanthanoids,” although they are commonly referred respectively] to as the “lanthanides.” The rare-earth element promethium (atomic number 61) is not included in discussions of REE deposits because the element is rare and Atomic Crustal Element Symbol unstable in nature. Yttrium (atomic number 39) is commonly regarded as an number abundance REE because of its chemical and physical similarities and affinities with the Light REEs lanthanoids, and yttrium typically occurs in the same deposits as REEs. Scandium Lanthanum La 57 39 (atomic number 21) is chemically similar to, and thus sometimes included with, the Cerium Ce 58 66.5 REEs, but it does not occur in economic concentrations in the same geological Praseodymium Pr 59 9.2 settings as the lanthanoids and yttrium and will not be discussed further. Neodymium Nd 60 41.5 Traditionally, the REEs are divided into two groups on the basis of atomic Samarium Sm 62 7.05 weight: (1) the light REEs are lanthanum through gadolinium (atomic numbers 57 through 64); and (2) the heavy REEs comprise terbium through lutetium Europium Eu 63 2.0 (atomic numbers 65 through 71). [Note: Some authorities include europium and Gadolinium Gd 64 6.2 gadolinium within the group of heavy REEs.] Yttrium, although light (atomic Heavy REEs number 39), is included with the heavy REE group because of its similar Terbium Tb 65 1.2 chemical and physical properties. Dysprosium Dy 66 5.2 Most REEs are not as rare as the group’s name suggests. They were named Holmium Ho 67 1.3 “rare-earth elements” because most were identified during the 18th and 19th Erbium Er 68 3.5 centuries as “earths” (originally defined as materials that could not be changed Thulium Tm 69 0.52 further by heat) and in comparison to other “earths,” such as lime or magnesia, they were relatively rare. Cerium is the most abundant REE, and is more common Ytterbium Yb 70 3.2 in the Earth’s crust than copper or lead. All of the REEs, except promethium, Lutetium Lu 71 0.8 are more abundant on average in the Earth’s crust than silver, gold, or platinum. Yttrium Y 39 33 However, concentrated and economically minable deposits of REEs are unusual. U.S. Department of the Interior Fact Sheet 2014 –3078 U.S. Geological Survey November 2014 How Do We Use the Rare-Earth Elements? Did you know.... Due to their unusual physical and chemical properties, such as unique magnetic and optical properties, REEs have Rare-earth magnets are stronger per unit weight diverse applications that touch many aspects of modern life and and volume than any other magnet type. Clean energy culture. Specific REEs are used individually or in combination technologies, such as large wind turbines and electric to make phosphors—substances that emit luminescence—for vehicles, use rare-earth permanent magnets (meaning many types of ray tubes and flat panel displays, in screens that permanently magnetized) that usually contain four REEs: praseodymium, neodymium, samarium, and dysprosium. range in size from smart phone displays to stadium scoreboards. Some REEs are used in fluorescent and LED lighting. Yttrium, europium, and terbium phosphors are the red-green-blue phosphors used in many light bulbs, panels, and televisions. rare-earth magnet. These magnets are also used in a variety of The glass industry is the largest consumer of REE raw conventional automotive subsystems, such as power steering, materials, using them for glass polishing and as additives that electric windows, power seats, and audio speakers. provide color and special optical properties. Lanthanum makes Nickel-metal hydride batteries are built with lanthanum- up as much as 50 percent of digital camera lenses, including based alloys as anodes. These battery types, when used in cell phone cameras. hybrid electric cars, contain significant amounts of lanthanum, Lanthanum-based catalysts are used to refine petroleum. requiring as much as 10 to 15 kilograms per electric vehicle. Cerium-based catalysts are used in automotive catalytic converters. Cerium, lanthanum, neodymium, and praseodymium, Magnets that employ REEs are rapidly growing in commonly in the form of a mixed oxide known as mischmetal, application. Neodymium-iron-boron magnets are the strongest are used in steel making to remove impurities and in the magnets known, useful when space and weight are limiting production of special alloys. factors. Rare-earth magnets are used in computer hard disks and The end use applications of REEs are detailed in USGS CD–ROM and DVD disk drives. The spindle of a disk drive Scientific Investigations Report 2011–5094 (available at attains high stability in its spinning motion when driven by a http://pubs.usgs.gov/sir/2011/5094/). Rare-earth elements (REEs) are used in the components of many devices used daily in our modern society, such as: the screens of smart phones, computers, and flat panel televisions; the motors of computer drives; batteries of hybrid and electric cars; and new generation light bulbs. Lanthanum-based catalysts are employed in petroleum refining. Large wind turbines use generators that contain strong permanent magnets composed of neodymium-iron-boron. Photographs used with permission from PHOTOS.com. Where Do Rare-Earth Elements Come From? sodium, potassium, and calcium. Many current (2014) advanced exploration projects are focused on large bodies of alkaline The REEs are commonly found together in the Earth’s igneous rocks, with some finding significant REE concentrations +3 crust because they share a trivalent charge ( ) and similar ionic (0.3 –2.6 percent total REE oxide). These deposit types are sought radii. In nature, REEs do not exist individually, like gold or because they are often enriched in the important heavy REEs. copper often do, but instead occur in minerals as either minor Ion-adsorption clay deposits in southern China are the or major constituents. In general, these minerals tend to be world’s primary source of heavy REEs. This deposit type is dominated by either light or heavy REEs, although each can informally referred to as “south China clays.” Thick clay accu- be present. In igneous (magmatic) systems, the large sizes of mulations that host low concentrations of REEs (from about the REE ions impede their ability to fit into the structure of 0.04 to 0.25 percent total REE oxides) form in tropical regions common rock-forming minerals. As a result, when common with moderate to high rainfall through successive processes: silicate minerals crystallize — such as feldspars, pyroxenes, 1. REEs are leached by groundwater from granite bedrock; olivine, and amphiboles— most REEs tend to remain in the coexisting magma. Successive generations of this process 2. thick zones of clay-rich soils develop above the granites; and increase REE concentrations in the residual magma until 3. mobilized REEs become weakly fixed (by ion-adsorption) individual REE minerals crystalize. The REEs can substitute for onto clays in the soils. one another in crystal structures, and multiple REEs typically Despite their low concentrations in REEs, the clay deposits occur within a single mineral. of south China are economic because the REEs can be easily REEs generally occur in uncommon geologic rock types extracted from the clays with weak acids, the deposits are often and settings. As mentioned earlier, REEs are common in the enriched in high-value heavy REEs, and labor costs are low.